Rewrite scratch buffer commands

+ No longer open persistent scratch buffers by default. Supply the
  universal argument to do that.

  SPC x = open throw-away scratch buffer
  SPC u SPC x = open persistent scratch buffer (prompted for file)

+ Added doom/delete-scratch-files

core/autoload/scratch.el

@@ -4,53 +4,74 @@
   "Where to store project scratch files, created by
 `doom/open-project-scratch-buffer'.")
 
+(defvar doom-scratch-buffer-display-fn #'display-buffer
+  "TODO")
+
 (defvar doom-scratch-buffer-hook ()
   "The hooks to run after a scratch buffer is made.")
 
-(defun doom--create-scratch-buffer ()
-  (let* ((project-p (doom-project-p 'nocache))
-         (text (and (region-active-p)
-                    (buffer-substring-no-properties
-                     (region-beginning) (region-end))))
-         (mode major-mode)
-         (derived-p (derived-mode-p 'prog-mode 'text-mode))
-         (project-root (if project-p (doom-project-root 'nocache)))
-         (id (projectile-project-name)))
-    (when (and id (string-empty-p id))
-      (user-error "Invalid id for a scratch buffer (%s)" id))
-    (unless (file-directory-p doom-scratch-files-dir)
-      (make-directory doom-scratch-files-dir t))
-    (with-current-buffer
-        (if project-p
-            (find-file-noselect
-             (expand-file-name (replace-regexp-in-string
-                                "\\." "_" id
-                                t t)
-                               doom-scratch-files-dir)
-             nil t)
-          (get-buffer-create "*doom:scratch*"))
-      (when project-p
-        (rename-buffer (format "*doom:scratch (%s)*" id))
-        (setq default-directory project-root))
+
+;;
+;; Library
+;;
+
+;;;###autoload
+(defun doom-scratch-buffer (&optional file mode text)
+  "Return a scratchpad buffer in major MODE with TEXT in it.
+
+If FILE is a valid path, open it as if it were a persistent scratchpad."
+  (if file (setq file (file-truename file)))
+  (let ((buffer
+         (if file
+             (with-current-buffer (find-file-noselect file)
+               (rename-buffer (format "*doom:scratch (%s)*" (file-name-nondirectory file)))
+               (current-buffer))
+           (get-buffer-create "*doom:scratch*"))))
+    (with-current-buffer buffer
       (when (and (not (eq major-mode mode))
-                 derived-p
                  (functionp mode))
         (funcall mode))
-      (if text (insert text))
+      (when text
+        (insert text))
       (run-hooks 'doom-scratch-buffer-hook)
       (current-buffer))))
 
 ;;;###autoload
 (defun doom/open-scratch-buffer (&optional arg)
-  "Opens a persistent scratch buffer in the same major-mode, at the current
-project root. If no project is found, scratch buffer will not be persistent. If
-a selection is active, copy it to the scratch buffer.
+  "Opens a scratch pad window in the same major-mode.
 
-If ARG (universal argument) is non-nil, display the buffer in the current
-window. Otherwise, display it in a pop up window.
+If ARG (universal argument), then open a persistent scratch pad buffer. You'll
+be prompted for its name, or to open a previously created. These are stored in
+`doom-scratch-files-dir'.
 
-Persistent scratch buffers are stored in `doom-scratch-files-dir'."
+If a region is active, copy its contents to the scratch pad."
   (interactive "P")
-  (funcall (if arg #'switch-to-buffer #'display-buffer)
-           (doom--create-scratch-buffer)))
+  (let (projectile-enable-caching)
+    (funcall
+     doom-scratch-buffer-display-fn
+     (doom-scratch-buffer
+      (when arg
+        (if-let* ((file (read-file-name "Open scratch file > " doom-scratch-files-dir "scratch")))
+            file
+          (user-error "Aborting")))
+      major-mode
+      (and (region-active-p)
+           (buffer-substring-no-properties
+            (region-beginning) (region-end)))))))
 
+;;;###autoload
+(defun doom/switch-to-scratch-buffer (&optional arg)
+  "Switches to a scratch pad buffer in the current window.
+
+Otherwise, does exactly what `doom/open-scratch-buffer' does."
+  (interactive "P")
+  (let ((doom-scratch-buffer-display-fn #'switch-to-buffer))
+    (doom/open-scratch-buffer arg)))
+
+;;;###autoload
+(defun doom/delete-scratch-files ()
+  "Deletes all scratch buffers in `doom-scratch-files-dir'."
+  (interactive)
+  (dolist (file (directory-files doom-scratch-files-dir t "^[^.]" t))
+    (delete-file file)
+    (message "Deleted '%s'" (file-name-nondirectory file))))